The present invention relates to memory modules which are typically employed in a processor based bus system; and, more particularly, the present invention relates to a filtering technique for reducing noise voltage on a reference voltage path in the modules.
There is an ever increasing trend to higher speed memory devices for use, for example, in processor based systems. In order to achieve high speed operation, data decisions within a memory device are often made based on a comparison of a data signal on a data path to a reference voltage VRef. To ensure accurate data detection, it is imperative that the reference voltage (VRef) be as stable and as reliable as possible.
Unfortunately, the reference voltage line in a bus system is subject to many interfering noise signals including noise signals originating from high speed switching circuits. These noise signals may impose an offset on the VRef which, in turn, can cause improper data recognition by the memory devices, .i.e., memory chips, on a memory module which uses the VRef.
The present invention is directed to a memory system which includes a plurality of memory modules, each of which has a filter thereon for filtering a VRef signal path. The filter is connected to a VRef input terminal of the module. The output of the filter supplies a filtered VRef signal to each of the memory devices on the module.
In another aspect, the filters of different memory modules may be cascaded together. To this end, the output of each filter is also connected to a filtered VRef output terminal of the module.